Impairments and disabilities - the difference: proposal for adjustment of the International Classification of Impairments, Disabilities, and Handicaps.

Key Words: Classification, Disability, Impairment, Physical disablement

Classifications, enabling the use of a uniform professional language, can be very useful in health care, for example, in the formulation of treatment goals, in the exchange of information and communication, and in research and education. The International Classification of Impairments, Disabilities, and Handicaps (ICIDH),[1] a classification that is internationally gaining wide acceptance in rehabilitation medicine, has a great potential for physical therapy practice in this respect.

The goal of language, enabling meaningful professional communication, can only be achieved if terms are used that have the same meaning and refer to the same concepts (units of thought[2]) for all persons involved in the communication. Vague, ill-defined, and ambiguous terms must be avoided as they hamper communication and are an obstacle to cooperation.[3] Uniformity of language can facilitate communication between physical therapists* and, for instance, insurance companies, patients, health care providers, and referring physicians about the contents, goals, and effects of physical therapy. Assuming a relationship between quality of communication and quality of care, a uniform professional language can enhance the quality of care provided by physical therapists. It is expected that the use of a uniform language facilitates developments, for example, in the areas of registration (record keeping), treatment protocols, and research into the effects of physical therapy interventions.

There is a great need in physical therapy for a uniform professional language based on a systematically developed set of concepts, Classifications, defined as "system[s] of concepts connected by generic relations,"[2] can contribute to the development of such a uniform professional language.

The World Health Organization (WHO), promoting the development and the use of classifications, has already developed a number of classifications for the medical profession.[1,4,5] In view of the different nature of the health care physical therapists and other health professionals provide, there is a need for classifications that meet the specific requirements of these professionals.

Classifications and Physical Therapists

Data

In physical therapy, many types of data are relevant (eg, referral data; name; address; place and date of birth; patients' complaints; examination findings; physical therapist's diagnosis; treatable components; treatment goals, characteristics, and results). As these data refer to different general concepts, their value is not available within a single classification. Several classifications, developed for separate concepts, are necessary to record the relevant data. In Table 1, the physical therapy process is divided into different phases. The data generated during these phases as well as the classifications that are necessary to classify these data are indicated. From Table 1 can be derived the idea that at least a "health status" classification, a "medical data" classification, a "procedures" classification, and a "technical aids" classification are necessary to classify the data relevant in the physical therapy process.

[TABULAR DATA 1 OMITTED]

To promote uniformity of language within health care in general, it is preferred to adapt, whenever possible, existing classifications in the development of classifications for health professionals. For this reason, we believe the ICIDH should be further developed until it is suitable for health professionals to describe the "health status" of their patients. With such a modified ICIDH, the patients' complaints, the examination findings, the treatable components, and, indirectly, the treatment goals and treatment results can be classified. The physical therapist's diagnosis, however, cannot be classified with the ICIDH alone, as will be explained in the next paragraph.

With regard to the "medical data" classification, use can be made of the International Classification of Diseases (ICD)[4] or the International Classification of Primary Care (ICPC).[6] To classify the patient's status after surgery, certain elements from the International Classification of Procedures (ICPM)[5] can be added (eg, to classify the patient's status after meniscectomy). With regard to a "technical aids" classification, use can be made of the ISO 9999, an international classification of technical aids for disabled persons.[7]

Diagnosis in Physical Therapy

Many articles have been devoted to diagnosis in physical therapy.[8-12] It is known that the medical information (referral data) that the physical therapist is provided with is often insufficient to guide the physical therapist's treatment.[13] This is comparable to the situation in rehabilitation medicine, in which patients are not necessarily treated on the basis of the medical diagnosis, but on the basis of present impairments, disabilities, and handicaps (classified using the ICIDH) and the extent to which these conditions prevent the patient from reaching his or her potential.[14] By performing their own evaluation, physical therapists are very often able to "refine" the medical diagnosis and formulate a physical therapist's diagnosis.

According to Jette,[10] the terminology of the ICIDH can be used for a physical therapist's diagnosis and classification; the three concepts of the ICIDH can be used to categorize clinical observations systematically and generate a diagnosis useful to physical therapy practice. Several authors[11,15] have described the physical therapist's diagnosis in terms of impairments, disabilities, and handicaps. Table 2 illustrates how "medical diagnosis" (classified with the ICPC) and "physical therapist's diagnosis" (in terms of impairments, disabilities, and handicaps) differ.[15] Patients with the same medical diagnosis (eg, low back pain or neck-shoulder pain) may have different impairments and disabilities. There is still debate, however, about the exact content and description of the concept "physical therapist's diagnosis," especially regarding whether the physical therapist's diagnosis is more than a just a combination of impairments, disabilities, and handicaps.

[TABULAR DATA 2 OMITTED]

In a recent article, the following definition of physical therapist's diagnosis was given:

... the professional opinion of a therapist

about the health status of a patient

taking into consideration the underlying

pathological process and based on

referral data, data from history, data

from physical examination and additional

medical and psychosocial 

data.[16(p20)]

Following this definition, the physical therapist's diagnosis is an opinion based on a thorough analysis of all data available, and consequently it will often be much more than just one or a list of impairments, disabilities, and handicaps. The discussion about the exact content of the concept of diagnosis in physical therapy still continues. A preliminary conclusion can be that the ICIDH seems to be an important tool for describing the health status of a patient, which is an important factor in the formulation of the physical therapist's diagnosis.

Based on the physical therapist's diagnosis, the therapist will determine which of the impairments and/or disabilities have to be treated and on which impairments or disabilities the treatment will initially focus. Treatment goals can be formulated using the terminology of the ICIDH. Naturally in the course of the treatment sessions, the physical therapist may decide to change his or her treatment approach and focus on other identified impairments or disabilities.

The degree or severity of many impairments and disabilities can be assessed with specific instrumentation.[17,18] Changes in severity, extent, and number of impairments and disabilities can be used as a measure of treatment efficacy (the difference between pretreatment and posttreatment).

ICIDH Versus ICD

The ICIDH, published by the WHO in 19801 as a classification "for trial purposes" and updated in 1993,[19] offers a conceptual framework for classifying a person's health status on three levels.[20] Impairments, disabilities, and handicaps are presented as three separate classifications, each describing the individual's health status from a different perspective. The concepts of the ICIDH are of a different nature than the concepts of the ICD. The ICD was developed to explain health problems. In the ICD, diseases, disorders, and complaints are classified according to etiology or organ system, basically for epidemiological and statistical purposes concerning morbidity and mortality. In contrast, impairments, disabilities, and handicaps are empirical concepts to describe health problems independent of the medical diagnosis. As stated by Halbertsma,[20,21] the ICIDH makes it possible to record health problems without taking into consideration their cause. With the ICIDH's Classification of Impairments, the health status of a patient can be recorded in medical terminology, for example, malformation or dysfunction at the organ level (including psychological functioning). With the ICIDH's Classification of Disabilities, functional limitations and activities/skills that cannot be performed are classified, and the ICIDH's Classification of Handicaps "translates" the results or effects of impairments and disabilities into dysfunctioning in socioeconomic roles.[20,22] The reader is referred to the article by Jette in this issue for further information about the structure of the ICIDH.

Criticism of the ICIDH

Although the ICIDH is being increasingly used in rehabilitation, in epidemiological surveys, and by policymakers,[23] many authors have indicated shortcomings and inconsistencies in the present ICIDH. These shortcomings and inconsistencies include overlap with the ICD; unclearness of the definitions of "impairment," "disability," and "handicap"; improper placement of several "impairments" and "disabilities"; violation of hierarchical rules and lack of a classification structure; presence of vague and ill-defined terms; absence of important impairments and disabilities; and problems in application of the ICIDH (eg, in classifying the results of the assessment of children, elderly patients, and patients with psychiatric disorders).[24] A major part of the criticism has been focused on the Classification of Handicaps.[22]

The criticism of the ICIDH comes from many areas of use of the ICIDH such as surveys, general rehabilitation,[25] psychiatry,[26] speech therapy,[27] rehabilitation of patients with low vision,[28] and audiology.[29] To help explain the criticism of the lack of a classification structure, an explanation of classification theory is necessary.

Classification Theory and the ICIDH

A classification system is an "arrangement of concepts into categories according to preset explicit criteria"[30] or, as indicated earlier, "a system of concepts connected by generic relations."[2] In a hierarchical classification, there is a step-by-step ordering of the concepts into classes and subclasses, from the general to the specific (Fig. 1). This ordering is based on one or more "types of characteristics." A type of characteristics is defined as a "genus of a characteristic," whereas a characteristic indicates "any of the qualities, properties or relationships which constitute a concept."[2]

According to classification rules, ordering should be carried out until further subdivision is no longer appropriate, resulting in "terminal classes," or classes that have no species varieties) in the same classification (eg, "disability in mounting a bike" in Fig. 1). Whether a further subdivision is appropriate depends on the target groups of the classification and, even more importantly, on the objectives of the classification. In, for instance, a population survey into the prevalence of disabilities in a certain community, it may be sufficient to record whether there is a "disability in locomotion" (class 6 in Fig. 1), whereas for research purposes, it may be necessary to know whether the patient is able to mount a bike, which is classified in class 6.4.1.1.1 (Fig. 1).

Most classifications serve several objectives; consequently, most classifications contain general, less detailed classes that are further subdivided into rather detailed subclasses. Whether the general classes or the detailed subclasses are used varies with the specific objective for application of the classification.

As the objectives of the ICIDH are not explicitly mentioned, and hence the domain of this classification--a set of all terms given a specific purpose[3]--is not known, it is impossible to criticize the level of detail chosen. As is the case with most medical classifications, the ICIDH is a compound hierarchical classification, which means that at a certain hierarchical level more than one type of characteristic is used in subdividing the classes at that level.[30] As shown in Figure 1, the types of characteristics at one hierarchical level (eg, tc2, tc3, and tc4) can be different. By adding a classification structure to the Classification of Impairments and the Classification of Disabilities, the presence of vague and ill-defined terms can be avoided, because the content of a class is primarily defined by the characteristics by which the class is created.

Update/Revision of the ICIDH

Because of the wide acceptance of the ICIDH as well as the criticism the classification has received, a revision of the ICIDH was initiated by the WHO in 1990.[19] Two centers were appointed as WHO collaborating centers for activities concerning the ICIDH, such as promotion of its use, collection and distribution of information, and contributing to the ICIDH revision process.

In 1992, the decision was made to publish an update of the ICIDH. This updating process resulted only in the correction of minor imperfections and the removal of the phrase "for trial purposes."[19] The real revision process began at the end of 1993.

The Classification Project

In 1990, the project "Classifications and Definitions of Concepts for the Health Professions" was started.[31] This project, referred to as the classification project, was initiated by the Dutch National Institute for Research and Postgraduate Education in Physical Therapy in collaboration with the national professional organizations of the five participating health professions and financed by the Dutch Ministry of Welfare, Health, and Cultural Affairs.

Phase 1 of the classification project focused on the formulation of a proposal for the adaptation of the Classification of Impairments and the Classification of Disabilities of the ICIDH.[32] The method used in phase 1 and some of the results are presented later in this article.

Phase 2 of the classification project was devoted to the development of the Draft for a Classification of Procedures, which was published in March 1993.[33] Phase 3 of the classification project was again directed at the ICIDH. This phase, in addition to serving as a commentary phase for the Draft Classification of Procedures, consisted of the following: 1. A critical analysis by representatives

of other disciplines of this proposal.

The preliminary results of

this analysis[34] are already incorporated

in the proposal for a revised

ICIDH, as presented in this article. 2. A critical review of the literature

pertaining to the ICIDH (on request

of the Dutch Collaborating

Center of the ICIDH) for the revision

meeting of December 1993,

including a list of the main criticisms

of the Classification of Impairments

and the Classification of

Disabilities.[35]

Method Used to Formulate a Proposal for Adjustment of the ICIDH

Based on the theoretical and practical considerations discussed, a procedure was developed in which the steps required for the development of proposals for a revised ICIDH were implemented in a logical way. After an analysis of the ICIDH, including an analysis of the definitions, adapted definitions and the domain (based on target groups and objectives for using the classification) were formulated. An extensive list of impairments and disabilities, falling within the formulated domain, was composed based on textbooks, articles, and activities-of-daily-living lists. Such comprehensive lists of terms are useful, because they give an impression of areas that are regarded as relevant and of the necessary detail. Using these lists, characteristics and types of characteristics forming the framework of a classification on the basis of which the terms (impairments and disabilities) are grouped into chapters, classes, and subclasses were formulated for both classifications separately. Using this framework, it was possible to place the collected impairments and disabilities in the appropriate classes. An extension (a subdivision) of a class was made whenever necessary to assign the impairments and disabilities.

The activities discussed were initiated by the representatives of the participating health professions, who were practicing therapists or teachers at colleges for health professions. Their task was to formulate proposals for each activity from the perspective of their own profession and representing the opinion of their own profession. The representatives of each profession in turn consulted with specialized colleagues in different fields of their profession, thus forming a group of "experts" for each profession. The activities of the representatives were coordinated by the project team, which was tasked with formulating a common point of view taking into account all comments from the representatives and experts, while adhering to the results of previous steps and classification rules. The effort resulted in a proposal for adjustment of the ICIDH, which was supported by the five participating professional organizations.

Suggested Changes for the Classification of Impairments and the Classification of Disabilities

The results of phase 1, including the adjustments made by other disciplines during phase 3, are summarized in this section.

Definitions and Domain

Definitions. Although the procedural guidelines for revision of the ICIDH mention that the definitions of impairment, disability, and handicap should remain unchanged,[36] several authors have criticized the definitions.[35] To overcome the difficulties in deciding whether a health problem should be called an impairment or a disability, slightly different definitions have been formulated, based on an analysis of the definitions as given in the ICIDH. Although the analysis will be published separately,[37] the reformulated definitions are presented in Table 3.

[TABULAR DATA 3 OMITTED]

Domain. For the Classification of Impairments, the following domain has been formulated:

1. Impairments that can serve directly

or indirectly as the object of care

by the health professions from a

preventive, curative, or palliative 

point of view.

2. Impairments that cannot be considered

as such, but that can lead to

impairments, disabilities, and handicaps

that can be the object of such

care.

3. Impairments that can influence the

choice of the therapeutic procedure(s)

or that can interfere with

the treatment result.

The domain for the Classification of Disabilities has been formulated similarly.[32,34]

Proposal for the Classification of impairments

An extensive inventory was made of impairments that were considered relevant to the participating health professions. Examples of impairments not present in the ICIDH are postural deviation (eg, of the vertebral column), hypotony of muscle, muscular atrophy, impairments in tissue properties, and impairments in postural reflexes.

A new chapter division is suggested for the Classification of Impairments (Fig. 2). Important changes include the following:

1. A combination of the impairments

of chapters 1 and 2 of the ICIDH

has been made in accordance with

the Classification of Intellectual and

Psychological Impairments (CIPI).[38]

Added to these impairments are

the impairments in structure and

function of the nervous system

very important for health professionals,

but absent in the ICIDH).

Examples of impairments of the

nervous system are discontinuity of

a nerve, decreased reflex activity,

and tingling. Impairments in other

systems resulting from impairments

in the nervous system are

placed in the chapters of the respective

systems (as in the present

ICIDH); for example, those visual

and hearing impairments resulting

from impairments in the nervous

system are placed in the chapters

relating to the eye and the ear.

2. The titles of chapters 3, 4, and 5 of

the ICIDH are renamed to give a

better indication of the content of

these chapters. The proposals of

Raaijmakers and Dekker[27] are incorporated

in the chapter "Voice,

Speech and Language Impairments,"

and those of Looijestein

and van Hof[28] are incorporated in

the chapter "Impairments of the

Eye and in Vision."

3. Chapter 6 ("Visceral Impairments")

is divided into six separate chapters

in the proposed adjustment to

the ICIDH, each pertaining to one

system. Impairments in the hormonal

and the immunological 

system, missing in the ICIDH, are

added. Impairments in smell and

taste (in chapter 9 of the ICIDH)

have been placed in the proposed

chapters 6 and 7, respectively (Fig.

2).

4. A new title and an extensive adaptation

of chapter 7 ("Skeletal Impairments")

are proposed. This

chapter, which is very important

for health professionals, is inadequate

in the current ICIDH and

needs total revision to meet the

demands of many of its users.[35]

5. The impairments in chapter 8

("Disfiguring Impairments") have

been reassigned to the appropriate

chapters and classes.

6. A new chapter is added, containing

impairments of the skin (in the

ICIDH, a small number of impairments

of the skin are incorporated

in chapter 8) and sensibility 

impairments.

The first type of characteristic for the Classification of Impairments has been based on the definition of impairment, resulting in two characteristics: (1) anatomical (structural) impairments and (2) functional (physiological and psychological) impairments. Because the ICIDH is primarily meant to describe the health status of an individual, regardless of the cause of the person's impairments, we decided to combine physiological and psychological impairments, as many impairments in function can have physiological as well as psychological components.

A set of characteristics and types of characteristics for both anatomical and functional impairments has been developed. In Fig. 3, the basic subdivision of the anatomical impairments is given. Examples are added of specific anatomical impairments of the locomotor system. In Fig. 4, the basic subdivision of the functional impairments is given, with examples of functional impairments of the respiratory system.

The proposal contains many more hierarchical levels than are shown in Figures 3 and 4; consequently a much more detailed division of the impairments is now available. All the impairments present in the ICIDH as well as the terms listed by the health professionals have been placed within the new structure.

Proposal for the Classification of Disabilities

An extensive inventory was made of disabilities that were considered relevant to the participating health professions, Examples of disabilities that are omitted in the current ICIDH are disabilities in recreational activities, in work/occupation and education, and in basic motor skills.

The new chapter division for the Classification of Disabilities is presented in Figure 5. As was indicated during the meeting for the revision of the ICIDH in November 1990, the Classification of Disabilities covers two broad disability types: functional limitations and activity restrictions.[36] Revision of the Classification of Disabilities should facilitate identification of the disabilities commonly referred to as functional limitations (disabilities in basic skills) and the more "complex" activity restrictions (disabilities in complex skills). in the proposed chapter division for the Classification of Disabilities, the disabilities in basic skills (chapters 1 and 2 and parts of chapters 3-5) are listed before the disabilities in the more complex skills (chapters 6-10). Some psychosocial skills such as participating in a group chapter 3) and some disabilities in communication skills (chapter 4) can be considered to form an intermediate category of disabilities.

The complex skills are divided into five broad categories (five chapters): (1) disabilities in personal care (including personal hygiene, toilet hygiene, sexual activities, dressing, eating/drinking, and attention to personal well-being), (2) disabilities in locomotion (including transferring oneself, moving, climbing, and private and public transportation), (3) domestic disabilities (including taking care of one's household, taking care of meals, taking care of clothing, handling the physical environment, taking care of housemates, taking care of pets, maintenance, and handling money or budgeting), (4) disabilities related to work or school (including the application of psychosocial abilities in the workplace or at school and handling circumstances related to work or school), and (5) disabilities in recreation (including performing physical activities, mental activities, artistic activities, and social activities). In Figure 6, the subdivision of the proposed chapter "Basic Motor Disabilities" is given, with some examples of specific disabilities.

Unlike the Classification of Impairments, in which the first type of characteristic is based on the definition of impairment, it was not possible to have a common type of characteristic for each chapter of the Classification of Disabilities, other than "kind of disability in . . . . " The proposal contains many more hierarchical levels than are shown in Figure 6; consequently, a much more detailed division of disabilities is now available, comparable to the example given in Figure 1. All the disabilities present in the ICIDH, as well as the terms listed by the health professionals, have been placed within the new structure.

Discussion

The ICIDH can be a very useful instrument for physical therapists to analyze the complaints of their patients, to record the examination findings in terms of impairments and disabilities, to formulate the objectives for physical therapy intervention and the treatable components on the basis of the formulated physical therapist's diagnosis, and to evaluate the results of treatment. Examples of the application of the proposals as given in this article are given in two articles by Gisbergen and colleagues[39,40] dealing with the reliability of diagnoses of impairments and disabilities by exercise therapists and chiropodists, respectively.

The level of detail used in describing the patient's health status, in terms of impairments and disabilities, depends both on the user and on the objectives for using the classification. The ICIDH can be used on a very general level for epidemiological purposes, whereas an effect study might demand a very thorough description of effect variables. These variables can be on the level of impairments (eg, pain, range of movement, anxiety), disabilities (eg, walking up and down stairs, bicycling, grasping, shopping, riding a bus, using a computer, horseback riding), and handicaps (eg, in social roles such as working, being a parent, and so forth). Consequently, the ICIDH should be useful on all levels of detail, demanding both a thorough choice of types of characteristics (considering the users and objectives) and the sequence in which they are used and a correct assignment of impairments and disabilities to the different classes based on a thorough analysis of their characteristics. If the revised ICIDH will satisfy these demands, data gathered at different places or for different objectives (level of detail) can be more easily compared.

The word "disability" means literally "not being able to." If an individual is not able to turn a key, wash his or her face, or walk, that person is "disabled" according to this interpretation. The WHO definition of disability fits the aforementioned examples. It seems, however, that especially in the American literature the word "disability" has a different, more "loaded" connotation, and is often used in a context in which, according to the WHO definition, "handicap" would be the appropriate term to use.[41-43]

Several authors have expressed concern about the "negative" approach of the Classification of Disabilities.[35] In the context of social medicine, social security benefits, and reemployment, it is important to know what an individual's capabilities are, instead of his or her inabilities.[44] Whether a positive or a negative classification is desired depends on the purpose for using the classification. Although the present proposal for the Classification of Disabilities contains disabilities, the classes are formulated in such a way that by deleting the prefix "dis," a positive classification arises.

In his model of "disease, impairment, functional limitation, and disability," Nagi[45] has introduced the level of functional limitation, between the level of impairment and the level of disability. During the first ICIDH revision meeting,[36] the recommendation was made to investigate the possibility of distinguishing, within the Classification of Disabilities, between functional limitations (basic skills) and activity restrictions (complex skills). In accordance with this recommendation in the proposal, the basic skills have been placed before the more complex skills (Fig. 5).

A Classification Anatomical Localization will be advantageous in order to be able to accurately indicate the localization of an impairment or a disease and the point of application of a procedure when appropriate. In order to study the efficacy of physical therapy interventions, it is essential that patient groups be matched not only for the medical diagnosis but also for impairments and disabilities.[46]

With an adapted Classification of Diseases, a revised version of the ICIDH, a Classification of Procedures,[33] and a Classification Anatomical Localization, it will be possible in the feature to select homogeneous groups of patients to assess the efficacy of physical therapy interventions. For example, to assess the efficacy of a modality or intervention (procedure + location) in the treatment of patients with a certain medical diagnosis (disease + location), the patients to be included in the study should have the same health status (impairment[s] + location, and disabilities).

Studies examining the efficacy of physical therapy interventions up to now have too often been conducted on patients who were selected on the basis of the medical diagnosis alone. In such subject selection, there exists a genuine danger in getting heterogeneously composed groups of patients in terms of number and extent of impairments and disabilities.[15] It is hoped that with the classifications mentioned in this article, the need for classifications, as expressed by Rothstein in his Editor's Note in the April 1993 issue of Physical Therapy, will be fulfilled, which will "in the end let us see what we did not see before and enable us to make meaningful comparisons."[47](p215)

Invitation

It is essential that health professionals cooperate in the development of classifications. Only in this way can classifications be developed that meet health professionals' specific requirements and needs. We would very much appreciate receiving comments on this article to improve the proposal as much as possible. Comments on the ICIDH may also be sent directly to the WHO or to one of the collaborating centers.[dagger]

Acknowledgments

We thank the representatives of the participating health professions for their contribution to the proposal presented in this article. We also thank Mrs HWA Wams (General Director of the Dutch National Institute for Research and Postgraduate Education in Physical Therapy) and Professor RAB Oostendorp, PhD, (Scientific Director of the Dutch National Institute for Research and Postgraduate Education in Physical Therapy) for their comments and suggestions in the preparation of this manuscript. [dagger] Comments on the ICIDH may be addressed to Dr MC Thuriaux, World Health Organization, Avenue Appica, CH-1211 Geneva 27, Switzerland; to NRV/WCC, Dutch Collaborating Centre for the ICIDH, PO Box 7100, 2701 AC Zoetermeer, the Netherlands; or to CTNERHI, French Collaborating Centre for the ICIDH, 2 Rue Auguste Comte, 92170 Vanues Cedex, France. (*) The terms "physical therapist" and "physical therapy" are used for the purposes of this article. theory and the proposals presented, however, are also applicable to occupational therapy, chiropody, and exercise therapy.

References

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YF Heerkens, PhD, is Human Movement Scientist, Dutch National Institute for Research and Postgradu Education in Physical Therapy (SWSF), PO Box 1161, 3800 BD Amersfoort, the Netherlands. Address all correspondence to Dr Heerkens.

JW Brandsma, PhD, is Physical Therapist, Dutch National Institute for Research and Postgraduate Education in Physical Therapy.

K Lakerveld-Hevi is Physical Therapist and Information Analyst, Dutch National Institute for Resea and Postgraduate Education in Physical Therapy.

CD van Ravensberg, PhD, is Physical Therapist and Human Movement Scientist, Dutch National Institute for Research and Postgraduate Education in Physical Therapy.

This work was supported by a grant from the Dutch Ministry of Welfare, Health, and Cultural Affair